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4

OPERATING

CONSIDERATIONS

PA51 • PA51A

GENERAL

Please read Application Note 1 "General Operating Con-

siderations" which covers stability, supplies, heat sinking,

mounting, current limit, SOA interpretation, and specification

interpretation. Visit www.apexmicrotech.com for design tools

that help automate tasks such as calculations for stability, in-

ternal power dissipation, current limit and heat sink selection.

The "Application Notes" and "Technical Seminar" sections

contain a wealth of information on specific types of applications.

Package outlines, heat sinks, mounting hardware and other

accessories are located in the "Packages and Accessories"

section. Evaluation Kits are available for most Apex product

models, consult the "Evaluation Kit" section for details. For

the most current version of all Apex product data sheets, visit

www.apexmicrotech.com.

SAFE OPERATING AREA (SOA)

The output stage of most power amplifiers has three distinct

limitations:

1. The current handling capability of the transistor geometry

and the wire bonds.

2. The second breakdown effect which occurs whenever the

simultaneous collector current and collector-emitter voltage

exceeds specified limits.

3. The junction temperature of the output transistors.

The SOA curves combine the effect of of all limits for this

Power Op Amp. For a given application, the direction and

magnitude of the output current should be calculated or mea-

sured and checked against the SOA curves. This is simple

for resistive loads but more complex for reactive and EMF

generating loads. The following guidelines may save extensive

analytical efforts.

1. Under transient conditions, capacitive and dynamic* induc-

tive loads up to the following maximums are safe:

CAPACITIVE LOAD

INDUCTIVE LOAD

±V

S

I

I

I

I

40V

400µF

200µF

11mH

4.3mH

35V

800µF

400µF

20mH

5.0mH

30V

1,600µF

800µF

35mH

6.2mH

25V

5.0mF

2.5mF

50mH

15mH

20V

10mF

5.0mF

400mH

20mH

15V

20mF

10mF

**

100mH

* If the inductive load is driven near steady state conditions,

allowing the output voltage to drop more than 8V below the

supply rail with I

I

should be capacitively coupled or the current limit must be

lowered to meet SOA criteria.

** Second breakdown effect imposes no limitation but thermal

limitations must still be observed.

2. The amplifier can handle any EMF generating or reactive

load and short circuits to the supply rail or shorts to common

if the current limits are set as follows at T

SHORT TO ±V

S

SHORT TO

±V

S

C, L, OR EMF LOAD

COMMON

45V

0.1A

1.3A

40V

0.2A

1.5A

35V

0.3A

1.6A

30V

0.5A

2.0A

25V

1.2A

2.4A

20V

1.5A

3.0A

15V

2.0A

4.0A

These simplified limits may be exceeded with further analysis

using the operating conditions for a specific application.

3.The output stage is protected against transient flyback. How-

ever, for protection against sustained, high energy flyback,

external fast-recovery diodes should be used.

CURRENT LIMIT

Proper operation requires the use of two current limit resis-

tors, connected as shown in the external connection diagram.

The minimum value for R

reliability it should be set as high as possible. Refer to the

“General Operating Considerations” section of the handbook

for current limit adjust details.

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This data sheet has been carefully checked and is believed to be reliable, however, no responsibility is assumed for possible inaccuracies or omissions. All specifications are subject to change without notice.

PA51U REV N MARCH 2005 © 2005 Apex Microtechnology Corp.